Patent application title: Interferometric Chemical Sensor Array

Abstract:

The device is a gas/vapor/aerosol/particulate sensor with a
receiver/transmitter option. This optical MEMS device is designed to be a
self-contained optical bench, integrating of an entire interferometer
into a MOEMS `optical bench` system-on-a-chip, and includes multiplexed
optical path sensors. The sensing structures consist of laser sources,
semiconductor photo detectors, refractive/reflective optical elements,
and specialized optical transmission paths. Each individual laser source
and photodiode is an optical path sensor with a particular
`functionalization.` These sensing arm functionalizations are sensitive
to unique chemical signatures and as a result can recognize and report
various chemical agents present in the ambient environment.

Claims:

1) An interferometric, single chip sensor comprising:a laser;a first
optical path having a functionalized sense arm open to an ambient
environment, the sense arm reactive to a preselected chemical signature;a
second optical path having a reference arm sealed from the ambient
environment;a beam splitter sending light emitted from the laser to both
the first and second optical paths whereby the chemical signature
reacting at the functional sense arm changes the first optical path
length relative to the second optical path length;a beam recombiner
creating a superposition of sense and reference beams yielding
interference fringes responsive to the change in the first optical path
length; anda photodetector for converting the interference fringes into a
detectable electrical signal.

2) The sensor of claim 1 wherein the sense arm is reactive to a plurality
of chemical signatures.

3) The sensor of claim 1 wherein the sensing functionalization of the
sense arm is selected from the group consisting of nanowires, aerogels,
aero-corals, crystal matrices, particulate meshes, catalyst meshes,
amorphous materials and treated fabrics.

4) The sensor of claim 1 wherein the functionalized sense arm further
comprises chemically reactive nanostructures open to the ambient
environment and the reference arm further comprises chemically reactive
nanostructures sealed from the ambient environment.

5) The sensor of claim 1 further comprising a wireless transmitter
communicatively coupled to the photodetector, the wireless transmitter
broadcasting data responsive to a predetermined value of the detectable
electrical signal converted by the photodetector.

6) A chemical vapor sensor array comprising:a plurality of interferometric
sensors on a single chip, each sensor specific to a preselected chemical
signature, each sensor comprising:a laser;a first optical path having a
functionalized sense arm open to an ambient environment and reactive to
the preselected chemical signature;a second optical path having a
reference arm sealed from the ambient environment;a beam splitter sending
light emitted from the laser to both the first and second optical paths
whereby the chemical signature reacting at the functional sense arm
changes the first optical path length relative to the second optical path
length;a beam recombiner creating a superposition of sense and reference
beams yielding interference fringes responsive to the change in the first
optical path length; anda photodetector for converting the interference
fringes into a detectable electrical signal,whereby the identity of the
chemical vapor is logically derived by one or more electrical signals
from the sensors.

7) The array of claim 6 further comprising a logic gate integral to the
chip, the logic gate activating a signal responsive to an identification
of the chemical vapor.

8) The array of claim 6 further comprising a wireless transmitter to
forward the one or more electrical signals from the sensors to a remote
logic processor for deriving the identity of the chemical vapor.

9) The array of claim 7 further comprising a wireless transmitter to
forward the signal to a remote receiver.

10) The array of claim 6 wherein the sense arm of at least one sensor on
the array is reactive to a plurality of chemical signatures.

11) The array of claim 6 wherein the chemical vapor sensor array is a
single use device whereby upon detection the electrical signals received
from the sensors the state of the electrical signals is maintained.

12) A chemical vapor sensor array comprising:a plurality of
interferometric sensors on a single chip, each sensor specific to at
least one preselected chemical signature to collectively identify a
chemical vapor, each sensor comprising:a laser;a first optical path
having a functionalized sense arm open to an ambient environment and
reactive to a sensor-specific preselected chemical signature;a second
optical path having a reference arm sealed from the ambient environment;a
beam splitter sending light emitted from the laser to both the first and
second optical paths whereby the chemical signature reacting at the
functional sense arm changes the first optical path length relative to
the second optical path length;a beam recombiner creating a superposition
of sense and reference beams yielding interference fringes responsive to
the change in the first optical path length; anda photodetector for
converting the interference fringes into a detectable electrical signal;a
logic gate integral to the chip, the logic gate deriving the identity of
the chemical vapor by one or more electrical signals from the sensor, the
logic gate subsequently activating a signal responsive to an
identification of the chemical vapor.

13) A chemical vapor sensor array comprising:a plurality of
interferometric sensors on a single chip, each sensor specific to a
unique preselected chemical signature, each sensor comprising:a laser;a
first optical path having a functionalized sense arm open to an ambient
environment and reactive to the sensor's unique preselected chemical
signature;a second optical path having a reference arm sealed from the
ambient environment;a beam splitter sending light emitted from the laser
to both the first and second optical paths whereby the chemical signature
reacting at the functional sense arm changes the first optical path
length relative to the second optical path length;a beam recombiner
creating a superposition of sense and reference beams yielding
interference fringes responsive to the change in the first optical path
length; anda photodetector for converting the interference fringes into a
detectable electrical signal,whereby the identity of the chemical vapor
is logically derived by one or more electrical signals from the sensors
against an empirically establish matrix of known chemical vapor signal
patterns.

[0003]This invention relates to a device designed to rapidly detect
harmful agents in the air. Specifically, the invention entails using
interferometers in sensing devices.

SUMMARY OF INVENTION

[0004]Non-MOEMS (Micro-Optical Electro-Mechanical System) chemical gas
vapor sensors are designed to detect agents affecting the nervous system,
the skin and mucous membranes, and the blood. These devices utilize a
spectroscopic technique that produces sensors that are bulky, heavy, and
difficult to transport. Moreover, these devices are high power
consumption sensors, requiring large power sources, further increasing
size and weight.

[0005]Interferometry is important for use in many precision sensing
applications including, but not limited to, physical signature
identification of gases and liquids. MOEMS interferometers have consisted
of discrete MOEMS devices, such as a detector serving as a `part` in a
larger macro-scale system design. State of the art devices still use
off-board sources, detectors and fiber optics.

[0006]Applications for MIOBS are important to researchers, and a
significant value is placed on the successful integrated miniaturization
of a complete stand-alone optical system-on-a-chip. Broader impacts of
this idea include immediate applications where small inexpensive gas and
fluid sensors are needed to fit in small places. Alternative embodiments
include not only precise position sensing of mirror displacement in
micromechanical systems, but also implementations such as strain gauges
and stand alone ring laser gyroscopes free from the physical, engineering
and production constraints associated with proof-mass systems.

[0007]Seeing an identifiable need, this invention discloses integration of
an entire interferometer into a MOEMS `optical bench` system-on-a-chip.
This optical MEMS device is designed to be a self-contained optical bench
on a single chip with multiplexed optical path sensors. The sensing
structures consist of laser sources, semiconductor photo detectors,
refractive/reflective optical elements, and specialized optical
transmission paths. Laser sources and their photo detectors are grown on
the substrate or can be bonded into place as drop-in dies. In some
embodiments, the device utilizes micron/nano-scale integration; space,
weight, power, on-board conditioning, processing and transmitter/receiver
electronics, element proximity and optical alignment, with scale sizes
approaching perceived `ultimate` physical constraints such as the
diffraction limit.

[0008]This invention comprises a MOEMS-based split beam interferometer, of
the Mach-Zehnder or Michelson type, in order to sense optical path length
differences between an exposed/vented object beam test arm and a `sealed`
reference beam arm. The interferometer comprises an optical coupler that
bonds to the source input line providing the laser source input light, a
beam splitter which splits the input signal into a sensing beam and a
reference beam and then provides a path for the sense and reference beam
to recombine thus producing the interferometers characteristic
superposition of waveforms and the ability to easily detect small shifts
in their output fringe patterns and convert this fringe shift into a
detectable electric signal. The reference arm is an optical replication
of the sense arm in its initial, undisturbed, null state. The sense arm
however is open to the ambient environment and the functionalization of
its optical path is designed such that it reacts in the presence of
certain chemical species, which are indicative of chemical agents, herein
termed `chemical signatures`. Both the sensing and the reference arms are
optical paths, such as light guides, constructed with standard
micromachining techniques, such as silicon fabrication methods and have
mirror structures at the end of their arms that reflect the light signal
back to the beam splitter which recombines the two beam causing waveform
superposition and the subsequent interference fringing in the detector
arm. When the interferometer is stabilized in its initial state, the
detector registers this initial input level which the system's
electronics registers and monitors. When a change in the optical path of
the sense arm takes place, as a result of chemically reacting with the
species for which it is sensitive, the interference fringe created by the
waveform superposition shifts and this shift in the interference fringe
at the detector results in a change in the detector's electrical output
level which the system flags as a positive reading and compares that
signal to the status of the rest of the sensing array and the system's
state.

[0009]An exemplary sensor according to an embodiment of the invention may
encompass an area of approximately one square inch and weighs 30 grams,
thus requiring less energy, and is encased in a translucent polymer that
makes it resistant to environmental extremes. The device is designed to
rapidly detect harmful chemical agents in the air, generally of minute
volumes of the targeted chemical measured in parts per trillion, by
replacing current devices with a single, small, portable microchip sensor
capable of being integrated into a uniform or personal equipment. The
construction of the device is based on MOEMS interferometer technology
that utilizes lasers incorporated on a silicon chip array to receive,
detect, and transmit results. The device may be multiplexed to detect
multiple chemical agents simultaneously, and possesses a
receiver/transmitter option.

[0011]The sensing functionalization may be comprised of nanowires,
aerogels, `aero-corals`, crystal matrices, particulate/catalyst meshes,
amorphous materials, treated fabrics, or other known means known in the
art, and may be implemented for reasons such as ease of fabrication,
better optical performance, and better sensitivity to the desired
chemical signature. The surfaces and chemical characteristics of these
nanostructures are chosen and engineered such that they provide active
sites, such as a strong alkali, for the target chemical agent to bind to
or react with. These chemical sites are also designed and chosen such
that the change due to the chemical reaction causes a sufficient change
in the optical path to be reliably detected, is well behaved from a
systems engineering approach and is not easily spoofed by spurious
signatures in the ambient environment.

[0012]The sensitivity of an embodiment of the invention may range from
parts per billion to parts per trillion of the target agent. The
described embodiment is small, lightweight, and convenient to carry. It
is contemplated that the device may be used with automotive safety and
control systems, industrial control and safety systems, home and building
sensing and control, fluidic sensors, agricultural monitors, vibration
sensors, magnetometers, and position sensors. The device may also be used
in a Sagnac ring interferometer for rotation sensing.

[0013]An embodiment of the invention comprises an interferometric, single
chip sensor having a laser, a first optical path having a functionalized
sense arm open to an ambient environment, the sense arm reactive to a
preselected chemical signature such as chlorine, cyanogens, sulfide,
phosphorus, fluoride or the like. The sense arm may be reactive to a
single chemical signature or may be relative to a plurality of chemical
signatures. The sensing functionalization of the sense arm may include,
but is not limited to, nanowires, aerogels, aero-corals, crystal
matrices, particulate meshes, catalyst meshes, amorphous materials and
treated fabrics. The sense arm may include chemically reactive
nanostructures open to the ambient environment while the reference arm
contains chemically reactive nanostructures sealed from the ambient
environment.

[0014]A second optical path having a reference arm is sealed from the
ambient environment using glass or nitride. A beam splitter sends light
emitted from the laser to both the first and second optical paths whereby
the chemical signature reacting at the functional sense arm changes the
first optical path length relative to the second optical path length.

[0015]A beam recombiner creates a superposition of sense and reference
beams yielding interference fringes responsive to the change in the first
optical path length and a photodetector converts the shift into a
detectable electrical signal.

[0016]A wireless transmitter communicatively coupled to the photodetector
may be provided. The wireless transmitter broadcasts data responsive to a
predetermined value of the detectable electrical signal converted by the
photodetector.

[0017]An alternative embodiment of the invention provides for a chemical
vapor sensor array. The array includes multiple interferometric sensors
on a single chip, each sensor specific to a preselected chemical
signature. The identity of the chemical vapor is logically derived by one
or more electrical signals from the sensors. The derivation may be made
not only from the positive signals of one or more sensors, but also from
the absence of a signal from one or more sensors.

[0018]A logic gate integral to the chip may be provided wherein the logic
gate activates a signal responsive to an identification of the chemical
vapor. Alternatively or in conjunction with the integral logic gate, a
wireless transmitter may forward the one or more electrical signals from
the sensors to a remote logic processor for deriving the identity of the
chemical vapor. A remote receiver may receive the forwarded signal to
coordinate a proper response to the chemical detection.

[0019]As the reactive nature of the sensing arm may lend itself to a
limited life-span, an embodiment of the invention anticipates that the
chemical vapor sensor array is a single use device whereby upon detection
the electrical signals received from the sensors, the state of the
electrical signals is maintained for confirmation of the results. A
timestamp value may be stored in conjunction with the firing of the
electrical signals.

[0020]Each sensor may be uniquely specific to at least one preselected
chemical signature to collectively identify a chemical vapor.
Alternatively, redundant sensors for the same chemical signature may be
provided on a single chip to mitigate the possibilities of false positive
signals.

[0021]In yet another alternative embodiment of the invention the identity
of the chemical vapor is logically derived by one or more electrical
signals from the sensors against an empirically established matrix of
known chemical vapor signal patterns. Alternatively stated, a library of
fingerprint signal collections is generated by exposing the array to
known chemical vapors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]For a fuller understanding of the invention, reference should be
made to the following detailed description, taken in connection with the
accompanying drawings, in which:

[0023]FIG. 1 is an elevated, isometric conceptual view of an embodiment of
the invention for detecting chemical vapor signatures using
Mach-Zehnder-type interferometer.

[0024]FIG. 2 is an elevated, isometric conceptual view of an embodiment of
the invention for detecting mechanical movement using Mach-Zehnder-type
interferometer.

[0025]FIG. 3 is an elevated, isometric conceptual view of an embodiment of
the invention for detecting chemical vapor signatures using
Michelson-type interferometer.

[0026]FIG. 4 is an elevated, isometric conceptual view of an embodiment of
the invention depicting a Michelson-type interferometer sensor with a
functionalization scheme in the open ambient sensing arm that is
replicated in the sealed reference arm.

[0027]FIG. 5 is an elevated, isometric conceptual view of an embodiment of
the invention comprising an array of Mach-Zehnder-type interferometer
sensors on a single chip.

[0028]FIG. 6 is a diagrammatic view of a logical process for deriving a
chemical identity from a plurality of interferometer sensor readings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029]Embodiments of the present invention may include
gas/vapor/aerosol/particulate interferometric sensors with a
receiver/transmitter options. All structures in the interferometric
sensor unit are intended to be fabricated with standard silicon
processing techniques (i.e. CMOS), including wafer level bonding and bulk
micromachining. The sensor is designed to rapidly detect harmful chemical
agents in the air with a single, small, portable microchip sensor, using
MOEMS interferometer technology that utilizes lasers incorporated on a
silicon chip array to receive, detect, and transmit results. Bonding pads
are used for the laser source input and photodetector output. Crystal
planes are envisioned, as well as corner reflectors. This optical MEMS
device is designed to be a self-contained optical bench on a single chip
with multiplexed optical path sensors. The sensing structures consist of
laser sources, semiconductor photo detectors, refractive/reflective
optical elements, and specialized optical transmission paths. Embodiments
of the invention may utilize a single lithium coin battery to provide
power for up to one year.

[0031]In FIG. 2, an embodiment of the invention employs a movable mirror
150 and a sense arm 160 open to the environment. Moveable mirror 150
aligned to sense arm 70A-B utilizes mechanical linkages 170 and allows
the optical path length to change in the sense arm 70A-B. This causes a
fringe pattern shift detected by photodetector 120.

[0032]In FIG. 3, an alternative embodiment of the invention is shown
utilizing Michelson topography wherein first mirror 180 at the end of
sense arm 70 and second mirror 190 at the end of reference arm 80 reflect
a beam from laser 30. Sensing window 200 in sense arm 70 reacts to
chemical signatures which are detected by photodetector 120. In FIG. 4,
forests of functional nanowires 210 are provided within both sense arm 70
and reference arm 80. However, functional nanowires 210 are sealed from
the ambient environment in reference arm 80.

[0033]In FIG. 5, an array of interferometer sensors 220A-D are provided on
single chip 20. Sensor 220A is specific to the detection of chlorine.
Sensor 220B is specific to the detection of cyanogens. Sensor 220C is
specific to the detection of sulfide. Sensor 220D is specific to the
detection of phosphorous. Responsive to exposure to the ambient
environment containing nerve agent VX, only sensors 220C and 220D
generate signals to logic gate 230. Logic gate 230 compares the received
signals to Table 1 (reproduced below) and generates a wireless
transmission via transmitter 240 that the presence of nerve agent VX has
been detected by the array.

[0035]Each individual laser source and photodiode is an optical path
sensor with a particular `functionalization,` as seen in FIG. 4. The
sensing functionalization is depicted as a forest of nanowires of optical
grade silica. These chemical sites are also designed and chosen such that
the change due to the chemical reaction causes a sufficient change in the
optical path to be reliably detected, is well behaved from a systems
engineering approach and is not easily spoofed by spurious signatures in
the ambient environment.

[0036]In addition to chemical functionalization, biological and other
functionalizations are possible. The success of other functionalizations
are based upon the capability of MEMS fabrication technology, optical
sensing constraints, and chem/bio agent physio-chemical characteristics.
Features such as thermal elements can also be added to optimize
sensitivity and packing arrangements can be made to resist extreme
environments. For instance, in one possible packing arrangement, the
sensor rests on a plastic base enclosed in a translucent polymer to make
it resistant to ambient environment extremes.

[0037]The laser sources and photo detectors are grown on the standard
silicon wafer processor or bonded into place as drop-in dies. Conductive
bonding pads are then attached for the connection of electronic power,
ground and signal. Each individual laser source and photodiode is an
optical path sensor with a particular `functionalization.` These sensing
arm functionalizations are sensitive to unique chemical signatures and as
a result can recognize various chemical agents present in the ambient
environment. The device may also utilize laser source signals via light
guides that the sensor inputs can opto-mechanically couple onto and also
provides the electrical routing for the fringe detect signal to the
output circuitry. Note that the array consists of as many different types
of functionalizations as necessary to cover a full "suite" of chemical
signatures. This detection matrix is depicted in Table 1.

[0038]The invention uses split beam pathways to detect biological or
chemical agents, but permits the detector to highly compact, thereby
allowing a user to wear the device. Upon sensing chemical agents, the
device alerts personnel to their presence and type. The alerts are both
in the proximity of the device via an audible alarm and remotely to a
tactical warfighter information network (WIN-T) net via intelligent
transmitter/receiver link. This capability is a result of current
fabrication technology which allows for receiver/transmitter sections and
control electronics to be placed on-board and adjacent to the sensor
arrays. The device can also be multiplexed to detect more than one
chemical agent, and possesses a receiver/transmitter option.

[0039]Soldiers can wear it on helmets, clothing, and armbands or it can be
attached to moving vehicles, planes, and trains. The device can easily be
modified to detect airborne biological warfare agents that may be
present. The device can detect chemical signatures in seconds.